1. Field of the Invention
This invention relates to optical fibers of the type commonly used for transmitting information by optical signals, and more particularly, to improving transmission in such fibers.
2. Description of the Prior Art
Optical fibers comprising at least a light-conducting core and a glass optical cladding thereon are generally coated with plastic materials in order to protect them against the detrimental effects of water vapor, which lead to stress corrosion cracking. However, plastic materials tend to limit the operation of optical fibers between about -50.degree. C. and +150.degree. C. The lower temperature boundary is dictated by considerations of flexibility; organic coatings tend to become brittle at lower temperatures. The upper temperature boundary is dictated by considerations of temperature stability; organic coatings tend to decompose at higher temperatures.
The use of metal coatings has enabled optical fibers to be employed in temperature applications which are limited only by the melting point of the metal coating. However, it has been observed that metallic-clad optical fibers show a substantial decrease in optical transmission as a function of increased temperature. Such transmission variations of optical transmission are, of course, unacceptable for optical fibers employed at elevated temperatures. As used herein, optical transmission includes at least the wavelength range from about 0.41 to 0.85 .mu.m.